foxy's picture


Observed: 7th March 2010 By: foxyfoxy’s reputation in Invertebratesfoxy’s reputation in Invertebratesfoxy’s reputation in Invertebratesfoxy’s reputation in Invertebrates

A small water beetle I observed to be behaving iratically in fast flowing gravelly water.It seemed to be rubbing itself of rocks in an attempt to dislodge the leechlike parasite attached to its head.

Species interactions

No interactions present.


John Bratton's picture

A tricky one. The pale stripe

A tricky one. The pale stripe down the edge of the elytra suggests Ilybius fuliginosus. But the contrast between the elytra and the black pronotum and the way the pale edge overflows on to the top surface of the elytra in the left-hand picture doesn't fit I. fuliginosus. Agabus paludosus is a possibility. Both these occur in running water. I'm not at home so can't consult the key or reference collection.

I agree it has a leech on its head.

Matt Smith's picture

Agabus ?

My immediate thoughts on looking at the photos was "Agabus", either A.sturmii or A.paludosus. It's not Ilybius fuliginosus, the shape is too broad and the "stripe" on the edge of the elytra is not continued onto the edge of the pronotum as is the case with I.fuliginosus. A better determination would need a look at a dry specimen.

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dshubble's picture


It's certainly superficially similar to both of these but I agree that it probably can't be identified further with any certainty, though in general a length measurement would be useful.

Carnivorous leeches generally go for softer and smaller prey than this, so maybe the beetle is just being used as some handy substrate - not identifiable beyond 'leech' though,


foxy's picture

Beetle I .D.

Thanks for the I.Ds.
The beetle was about 9-10mm and I should have included it earlier.Although it was in gravelly water I think this was mainly due to its distress at the leeches attachment ,in still muddy bottomed water up and downstream lots of similar beetles were in evidence and no other live form was present at the gravel that I could see.



Martin Harvey's picture


Both Colymbetes fuscus and Hydaticus seminiger are larger than the 9-10mm size that Foxy has given for this one. On that basis Agabus is looking the most likely, but I'm going to cop out and stick with Dytiscidae!

Entomologist and biological recorder

John Bratton's picture

Its not clear whether 9-10 mm

Its not clear whether 9-10 mm was an estimated afterthought, or was actually measured.

foxy's picture

9-10 mm

It did not measure it but would be good at estimating its lenght it was uploaded about 30 mins after I saw it and lenght added following day .


John Bratton's picture

I think there is too much

I think there is too much black on the pronotum for Hydaticus seminiger.